This invention relates to an apparatus for dissolving air in water and subsequently reducing the surface tension of the water in flotation systems, particularly for the treatment of waste water and sludges, whereby the air is dissolved in pressurized water which is then led out of a pressurized container to a flotation basin by means of a surface tension reducing device.
Flotation is a method by which particles of materials contained in liquids which are difficult or impossible to settle out can be separated out with the aid of extremely small air bubbles; the bubbles introduced into the liquid adhere to the particles and carry them to the surface of the liquid. Full current, partial current and return flow flotation methods are known. In the full current method the entire quantity of liquid is led into a pressurized container and the surface tension thereof is reduced after saturation. In the partial current method only a portion of the liquid quantity is enriched with air in the pressurized container and added to the remaining portion of the liquid after the surface tension reduction. According to the return flow method a portion of the discharged clean water from the flotation or other cleaned water is enriched with pressurized air and is added to the liquid to be cleaned having had its surface tension already reduced.
A flotation system with a pressurized container is known in which air is dissolved in pressurized water stored therein. The air is pressed into the feed pipe of the container by means of a compressor on the pressure side of pumps which feed the water into the container. The air-enriched water from the container travels through a surface tension reduction device into the flotation basin.
Further, a flotation system with a pressurized container is known in which pressurized water saturated with air is produced and stored. The water is delivered under pressure into the container through a pipe. The pipe opens concentrically in the narrowing portion of a venturi nozzle which is connected with the air by means of an aspiration tube. The expanding portion of the venturi nozzle is downwardly directed and ends in the lower portion of the water container. The water is drawn out through an opening in the container. At the upper portion of the container there is a pipe with a valve through which excess air not dissolved in the water is removed from the container (German OS No. 2,358,077).